This project consists of an investigation of the maturation of thymus-derived lymphocytes. In the coming year attention will be focussed on T lymphocyte precursors, as detected in mouse bone marrow. Three developmental stages of precursors have been identified, using the cells' interactions with the mitogen concanavalin A as a marker. It is hoped that a developmental model for these cells can be constructed, as has been done for other hematopoietic cells.